Keaton’s odds were astronomical heading into Sunday night’s SAG Awards, with Redmayne trailing in second place. Then the envelope was opened and all hell broke loose. To call the win unexpected would be an understatement; in fact, Gold Derby’s very own Tom O’Neilwas the only expert to predict it.

I myself had Redmayne at number-one for months before it became clear that “Birdman” was a more popular film within the industry than “The Theory of Everything,” and now I’m been kicking myself for switching to Keaton.

But before I take the plunge with the rest of our experts (indeed, the odds have already started to change; click here to see the drastic shift in our graphs), let’s take a minute to think about what this all means.

This has been a two-horse race from the very beginning. Both actors won Golden Globes, Keaton in the Musical/Comedy category, Redmayne in Drama. Keaton then won the Critics’ Choice Award, thus putting him on course to continue his momentum with a SAG victory. But SAG voters went their own way and rewarded Redmayne, and it should be noted that since 1994, when the guild first started handing out prizes, the SAG recipient has gone on to triumph at the Oscars an astounding 16 times. They are:

Judging from that track record, Redmayne should obviously be at number-one right now. You’ll notice, however, that there was an odd four-year period where SAG and Oscar didn’t align. Those winners were:

– Benicio Del Toro, “Traffic” (2000), Oscar went to Russell Crowe (“Gladiator”) though the academy did award Del Toro in the supporting race

Let’s analyze those disparities and how they may relate to this year’s race:

2000
As we learned from Kate Winslet in “The Reader” (2008), academy voters can put you wherever they like on their nominations ballot, even if you were competing in another category at precursor events. Such was the case with Benicio Del Toro, who was nominated as a lead at SAG and supporting at the Oscars for his turn in “Traffic.” And like Winslet – albeit the other way around – Del Toro won both prizes. This allowed Russell Crowe to squeeze past Globe-winner Tom Hanks (“Cast Away”) to triumph at the Oscars for “Gladiator.”

But category confusion isn’t a problem this year, so we can eliminate this as a possible scenario, though it should be noted that Crowe was in a Best Picture frontrunner, which could work in Keaton’s favor.

2001
With SAG, BAFTA, and Golden Globe victories for “A Beautiful Mind,” Russell Crowe was well on his way to becoming the third person in history to win back-to-back Best Actor Oscars (after Spencer Tracy and Tom Hanks). But Crowe caused a scandal when he threw a phone at a hotel desk clerk, which brought him enough negative publicity to open the door for Denzel Washington to become the first black Best Actor-winner since Sidney Poitier (“Lilies of the Field,” 1963), and to date the only black actor to win twice (his first was in Supporting Actor for “Glory” in 1989).

No such phone-throwing incident has occurred this year (though the season is still young), so for now we can scrap this scenario as well.

2002
Now here’s where things get interesting. In 2002, the Best Actor race seemed to be split between Jack Nicholson for “About Schmidt” and Daniel Day-Lewis for “Gangs of New York.” Nicholson won the Globe, while Day-Lewis won SAG. The odds quickly tipped in Day-Lewis’s favor when he repeated at the BAFTAs, but Adrien Brody pulled off an upset for “The Pianist,” perhaps because the two veterans split the vote. Could we be looking at another surprise this year?

If there is an upset, it could be Bradley Cooper, currently in third place with 20/1 odds for the box-office bonanza “American Sniper.” This is his third consecutive nomination (fourth if you count his Best Picture nod for producing the film), his second in the lead category, and this time he got in with zero precursor support. Yet therein lies the problem: no one – and I mean no one – has ever won Best Actor without a SAG nomination. There have been instances of this occurring in the supporting races (twice, in fact: Marcia Gay Harden in “Pollock” in 2000, and Christoph Waltz in “Django Unchained” in 2012), but Cooper would be the first lead performer to do so.

2003
Here’s another scenario we often see play out, in which the two frontrunners both win Golden Globes. In 2003, Bill Murray triumphed in the Musical/Comedy category for “Lost in Translation,” while his chief competition, Sean Penn in “Mystic River,” won in Drama. All eyes were on SAG to help clear things up, but they only confused matters further by rewarding fellow Globe Musical/Comedy nominee Johnny Depp for the first installment of the “Pirates of the Caribbean” franchise. Although Murray emerged victorious at the BAFTAs, Penn took the Oscar, perhaps due to the fact that voters took his dramatic performances more seriously than his more comic rivals.

The same could be true of Redmayne in “The Theory of Everything,” who as scientist Stephen Hawking must portray a disability and undergo a stunning physical transformation. If you want to go mining for Oscar gold, there are worse ways you could go about it.

But let’s now turn our attention to a year where there wasn’t a disparity, but no doubt that it was a close race. I’m speaking of 2011, when for months George Clooney was the predicted front-runner for “The Descendants.” Clooney won Critics’ Choice and the Globe for Best Drama Actor, but lost SAG and the Oscar to Jean Dujardin for “The Artist.” That was a rare instance of a Globe-winner in the Musical/Comedy category beating out his dramatic rival. The big difference there was that Dujardin’s film was in the lead for Best Picture. That could be good news for Keaton; “Birdman’s” SAG Best Ensemble and PGA Best Picture wins make it a possible frontrunner at the Oscars.

Additionally, Keaton’s got a lot going for him: a long career that’s in an upswing, several critics and industry prizes, and many friends in the business who would love to see him clutching a gold statuette. It should be noted that the SAG Awards are voted on solely by actors, many of whom aren’t academy members, whereas Oscar-winners are voted on by a wide variety of Hollywood professionals. Perhaps SAG felt his ensemble win was reward enough and wanted to spread the wealth. If “Birdman” is slowly becoming the Oscar frontrunner, then Keaton – who gets credit for a great deal of the film’s success – could get swept up in a wave of support.

Yet Redmayne has a lot going for him as well: as stated above, he gives a performance that requires a lot of technical craft, and oftentimes he’s tasked with conveying his character’s innermost thoughts and feelings through use of his eyes alone. Actors, who understand the challenges that come with such roles, were no doubt impressed, which accounts for his SAG win. It stands to reason that others in the academy – not just actors – would also be blown away by his portrayal. And like “Birdman,” “The Theory of Everything” is a Best Picture contender.

Our attention now turns towards BAFTA. It’s suicidal to bet against the British Redmayne at the BAFTAs, and indeed, the tide may be turning in his favor overall. But one thing is certain: with its many twists and turns, this is shaping up to be the most exciting Best Actor race in years.